Cylinder head and motor block castings

ABSTRACT

The present invention relates to a cylinder head and motor block casting and a method of making the same, including an aluminum alloy having the following composition: Si 6.80-7.20, Fe 0.35-0.45, Cu 0.30-0.40, Mn 0.25-0.30, Mg 0.35-0.45, Ni 0.45-0.55 Zn 0.10-0.15, Ti 0.11-0.15 with the remainder being aluminum as well as unavoidable impurities with a maximum content of 0.05 each, but not more than a maximum of 0.15 impurities in all.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a cylinder head and motor blockcasting, including an aluminum alloy having the following composition:Si 6.80-7.20, Fe 0.35-0.45, Cu 0.30-0.40, Mn 0.25-0.30, Mg 0.35-0.45, Ni0.45-0.55 Zn 0.10-0.15, Ti 0.11-0.15 with the remainder being aluminumas well as unavoidable impurities with a maximum content of 0.05 each,but not more than a maximum of 0.15 impurities in all.

[0003] 2. Description of the Related Art

[0004] The properties of aluminum depend on a number of factors wherebyadded or accidentally present admixtures and impurities of otherelements play an important part. The main alloying elements are copper(Cu), silicon (Si), magnesium (Mg), zinc (Zn) and manganese (Mn).

[0005] It often happens that the following impurities or additions arecontained in small quantities: iron (Fe), chromium (Cr) and titanium(Ti). The following additions are used for special alloys: nickel (Ni),cobalt (Co), silver (Ag), lithium (Li), vanadium (V), zirconium (Zr),tin (Sn), lead (Pb), cadmium (Cd) and bismuth (Bi).

[0006] All alloy constituents are completely solvable in liquid aluminumat a high enough temperature. The solubility in the solid state withformation of solid solutions is limited for all elements; there is noalloy system comprising aluminum which shows a uninterrupted solidsolution sequence. The unsolved parts form their own phases, so-calledheterogeneous constituents, in the alloy micro structure. They are oftenhard and brittle crystals made up of one element alone (e.g. Si, Zn, Sn,Pb, Cd, Bi) or consisting of intermetallic compounds comprising aluminum(such as Al₂Cu, Al₈Mg₅, Al₆Mn, Al₃Fe, Al₇Cr, Al₃Ni, AlLi). Alloys havingtwo or more constituents contain in addition to these intermetalliccompounds, yet other intermetallic compounds consisting of the additions(e.g. Mg₂Si, MgZn₂), ternary phases (e.g. Al₈Fe₂Si, Al₂Mg₃Zn₃, Al₂CuMg)and phases comprising even more constituents. The formation of solidsolutions and the formation of the heterogeneous micro structureconstituents (their amount, size, form and distribution) determine thephysical, chemical and technological properties of an alloy. Due to thefact that the diffusion rate decreases with temperature it is possible,after a rapid cooling from higher temperatures, that Al-solid solutionsmay contain higher levels of solved elements than would be possible inequilibrium at room temperature. In such over saturated solid solutionsprecipitation processes may occur at room temperature or at moderatelyraised temperatures (partly with formation of metastable phases), thesemay be of great influence on the properties. Elements which diffuseslowly such as Mn can be over saturated far beyond the maximumequilibrium solubility by rapid solidification from the melt. This oversaturation may be remedied by annealing at high temperatures. Theadditions are then precipitated in a finely dispersed manner. Often thisannealing process (full annealing) is used for compensating microsegregation.

[0007] Below some important binary and ternary systems are describedwith short explanations:

[0008] Aluminum-copper

[0009] In the range of 0 to approximately 53% Cu there is a simpleeutectic sub-system with a eutetic at 33.2% Cu and 547° C. The maximumsolubility at the eutectic temperature in the alpha solid solution is5.7%. The solubility decreases with falling temperature and is only0.45% at 300° C. Unsolved copper is present in the form of Al₂Cu in thestate of equilibrium. Metastable transition phases may be formed atmedium temperatures by precipitation from the oversaturated solidsolution.

[0010] Aluminum-silicon

[0011] This system is purely eutectic having a eutetic at 12.5% Si and577° C. At this temperature 1.65% Si are solvable in the alpha solidsolution. At 300° C. only 0.07% are solvable. The crystallisation ofeutectic silicon may be influenced by small amounts of additions (e.g.of sodium or strontium). In this case an overcooling and shift ofconcentration of the eutectic point occur in dependence on thesolidification rate.

[0012] Aluminum-magnesium

[0013] The subarea between 0 and approx. 36% Mg is eutectic. The euteticis at approximately 34% Mg and 450° C. At this temperature the (maximum)solubility is 17.4% Mg. At 300° C. 6.6% and at 100° C. about 2.0% Mg aresolvable in the alpha solid solution. In most cases unsolved Mg ispresent in the microstructure in the form of the B-phase (Al₈Mg₅).

[0014] Aluminum-zinc

[0015] The alloys form a eutectic system having a high-level zinceutetic at 94.5% Zn and 382° C. In the area high in aluminium, which isof interest here, 31.6% Zn are solvable at 275° C. in the solidsolution. The solubility is very much dependent on the temperature andfalls to 14.5% at 200° C. and to 3.0% at 100° C.

[0016] The systems of aluminum-manganese, aluminum-iron andaluminum-nickel show a eutetic at a low concentration. The melting pointis only very slightly lowered. The solubility in the solid state is lowexcept that of manganese.

[0017] From the journal AFS Transactions, Volume 61, 1998, pages 225 to231, it has been known to optimize aluminum-silicon cast alloys forcylinder heads by adding copper to them. In this case the thermalstrength of an AlSi₇Mg-alloy, to which 0.5 to 1% copper had been added,increased significantly whereby simultaneously the creep resistance alsoimproved. The improvement of the mechanical properties, however, isaccompanied by a deterioration of ductility and a reduced corrosionresistance.

[0018] After having manufactured the cylinder head and motor blockcastings in a casting process it is often necessary to carry outmachining operations on them. In certain alloys problems occur as aresult of too little hardness because the surfaces of the castingsbecome very soft so that fine scoring or smudging may occur.

[0019] Furthermore, such alloys must have a high thermal conductivity sothat the castings are suitable for use in motors. The piston alloys with12% Si which have been examined by way of comparison do not meet therequirements, nor does the normally used AlSi9Cu3.

SUMMARY OF THE INVENTION

[0020] Therefore, an object of the present invention is to provide analloy suitable for use in cylinder head and motor block castings, havinga high thermal conductivity and an appropriate crystalline structure,high thermal strength, good creep resistance as well as sufficientductility and, at the same time, having low vulnerability to corrosionand being easily machinable.

[0021] According to the present invention this object is accomplished bythe features in the claims.

[0022] The research of the inventors has shown that cylinder head andmotor block castings consisting of an aluminum alloy comprising thefollowing composition:

[0023] Si 6.80-7.20

[0024] Fe 0.35-0.45

[0025] Cu 0.30-0.40

[0026] Mn 0.25-0.30

[0027] Mg 0.35-0.45

[0028] Ni 0.45-0.55

[0029] Zn 0.10-0.15

[0030] Ti 0.11-0.15

[0031] remainder aluminum as well as unavoidable impurities with amaximum content of 0.05 each, but not more than a maximum of 0.15impurities in all, exhibits an especially high creep resistance andthermal strength, if phases in the amounts of 1 to 3 vol. % of thealuminum-nickel type, aluminum copper type, aluminum-manganese type,aluminum-iron type and mixed phases of the aforementioned types arecontained and if, in particular, a ratio of Ni:Mg:Cu=5:4:3.5 isobserved. The thermal conductivity and ductility of a cylinder head andmotor block casting are improved by a crystalline structure consistingof an alpha aluminum matrix structure having 40 to 55 vol. % and byobserving a Mn/Fe-ratio of at least 0.781. If the aluminum alloyelements are contained in the following ratios

[0032] Si:Fe:Cu=7:0.4:0.35

[0033] Ni:Mg:Cu=5:4:3.5

[0034] the cylinder head and motor block casting according to thepresent invention shows very good corrosion properties. It was foundthat cylinder head and motor block castings are easier to machine andhave an improved hardness when they are produced in the following way:

[0035] An aluminum alloy is filled into a casting mold at a temperatureof 720° to 740° C., then the aluminum alloy is subjected to cooling at acooling rate of 0.1-10 K s⁻¹ and after cooling to room temperature athermal treatment is carried out consisting of a solution heat treatmentat 530° C. for 5 hours, chilling in water at 80° C. and artificialageing at a temperature of 160 to 200° C. for 6 hours.

[0036] Several examples of embodiments are given below, from which theprocessing advantages become obvious which result from an increasedhardness and a better machinability combined therewith as well as areduced vulnerability to corrosion while the good mechanical propertiesare maintained (Table 1). A nickel-alumiumium alloy known from theAluminum-Taschenbuch 14th Edition, page 35 was examined as comparisonexample to the alloys according to the present invention. It was foundthat only a low thermal conductivity could be measured due to the higheutectic portion.

[0037] The assessment of the processibility is based on a comparison ofhardness wherein the individual values were obtained in an indentationtest according to Brinell. For the alloy according to the presentinvention a hardness of 100 to 105 HB was measured in contrast to 85 to90 HB for the compared alloy.

[0038] The particularly high degree of hardness measured for the alloyof the invention could be achieved by a special artificial ageing as itis defined in claim 4. In this treatment the following parameters wereobserved:

[0039] casting temperature: 730° C.

[0040] cooling rate: approx. 1 to 5 K/s

[0041] solution heat treatment at 530° C. for 5 hours

[0042] chilling in water of 80° C.

[0043] artificial ageing at 180° C. for 6 hours

[0044] A corrosion comparison with a copper-containing alloy (0.5%copper of alloy No.6) showed a distinctive improvement of the corrosionresistance (in view of the State of the Art) and especially in view ofthe conventionally used alloys, such as alloy No. 5 which has so farbeen used for the production of cylinder heads and motor block castings.Thus, it may be assumed that the use of the alloy according to thepresent invention results in achieving a substantial improvement of thecorrosion properties when copper is replaced by nickel, wherein thespecial thermal treatment as previously described and the concentrationlimits as defined in claim 1 helped in the advantageous formation of thephases (i.e. in the extensive spheroidizing of the phases) of thealuminum-copper type and the magnesium-silicon type.

[0045] The obtained degrees of hardness were not only decisivelyinfluenced by the individually used phase types but also by theirdistribution and fineness as well as their amounts measured in volumepercent. The amount was determined by means of quantitative imageanalysis of statistically distributed sections, whereas the phase typeswere determined by micro probe examination. While State of the Art alloyNo. 6 (Table 1) contained only 0.5 vol. % of the Cu-containing phase,the alloy of the present invention shows finely distributedintermetallic phases of an average length of 20 μm maximum of the typesaluminum-nickel, aluminum-copper and aluminum-iron-manganese, whereinthe volume proportion was at least 1 vol. % which is to be considered animportant reason for the improvement in thermal strength.

[0046] Thus, while there have been shown and described and pointed outfundamental novel features of the invention as applied to a preferredembodiment thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the devicesillustrated, and in their operation, may be made by those skilled in theart without departing from the spirit of the invention. For example, itis expressly intended that all combinations of those elements and/ormethod steps which perform substantially the same function insubstantially the same way to achieve the same results are within thescope of the invention. Substitutions of elements from one describedembodiment to another are also fully intended and contemplated. It isalso to be understood that the drawings are not necessarily drawn toscale but that they are merely conceptual in nature. It is theintention, therefore, to be limited only as indicated by the scope ofthe claims appended hereto. TABLE 1 Distribution of phases HardnessCorro- Si Fe Cu Mn Mg Ni Zn Ti Si:Fe:Cu Fe:Mn Mg:Ni HB sion Invent. 6.80.35 0.30 0.25 0.35 0.45 0.10 0.11 7:0.4: 1:0.7 4:5 105 + Alloy 1 0.35Invent. 6.93 0.38 0.33 0.26 0.38 0.48 0.12 0.12 100 + Alloy 2 Invent.7.07 0.41 0.37 0.28 0.42 0.52 0.13 0.13 102 + Alloy 3 Invent. 7.20 0.450.40 0.30 0.45 0.55 0.15 0.15 104 + Alloy 4 Compar. 8.86 0.650 2.400.520 0.27 0.010 0.270 0.121 — — —  90 − Alloy 5 Compar. 7.13 0.125 0.500.005 0.36 0.004 0.006 0.007 — — —  85 − Alloy 6

What is claimed is:
 1. A cylinder head and motor block casting,comprising an aluminum alloy having the following composition: Si6.80-7.20 Fe 0.35-0.45 Cu 0.30-0.40 Mn 0.25-0.30 Mg 0.35-0.45 Ni0.45-0.55 Zn 0.10-0.15 Ti 0.11-0.15, the remainder being aluminum andimpurities of a maximum content of 0.05 each, but not more than amaximum of 0.15 impurities in all, and wherein at least 1 vol. % of thefollowing phases of the aluminum-nickel type, aluminum-copper type,aluminum-manganese type, aluminum-iron type and mixed phases of theaforesaid types.
 2. The cylinder head and motor block casting accordingto claim 1, having the following crystalline structure a) an alphaaluminum matrix structure having 40 to 60 vol. %; b) an eutecticaluminum-silicon phase having 40 to 55 vol. %; and c) further phasescomprising 1 to 3 vol. % of aluminum and alloying constituents iron,copper, magnesium, nickel and silicon.
 3. The cylinder head and motorblock casting according to claim 2, wherein the ratios of the aluminumalloy elements are as follows: a) Si:Fe:Cu=7:0.4:0.35; b) Fe:Mn=1:0.7;and c) Ni:Mg:Cu=5:4:3.5.
 4. A method for manufacturing a cylinder headand motor block casting, including an aluminum alloy having Si6.80-7.20, Fe 0.35-0.45, Cu 0.30-0.40, Mn 0.25-0.30, Mg 0.35-0.45, Ni0.45-0.55, Zn 0.10-0.15, Ti 0.11-0.15, the remainder being aluminum andimpurities of a maximum content of 0.05 each, but not more than amaximum of 0.15 impurities in all, and wherein at least 1 vol. % of thefollowing phases of the aluminum-nickel type, aluminum-copper type,aluminum-manganese type, aluminum-iron type and mixed phases of theaforesaid types, comprising the step of a) filling an aluminum alloyinto a casting mold at a temperature of 720° to 740° C.; b) cooling thealuminum alloy at a cooling rate of 0.1 to 10 K s⁻¹; c) carrying out athermal treatment after the cooling to room temperature is accomplishedby providing a solution heat treatment at 530° C. for 5 hours; andchilling in water at 80° C. and artificial ageing at a temperature of160 to 200° C. for 6 hours.